P.S.
As far as ridgidity is concerned , the prepreg cf tubes that i get from my supplier have an 80% unidirectional(longitudinally) fibre content , and a sligthly higher fibre-to-resin ratio than can be achieved by the pulwining/pultrusion process . As for the stiffness of bits from a fishingrod , that would be highly dependent on the diameter and type of rod . That said , a short length as would be necessary for a linear tracking tonearm , 4 to 6 inches for example , would require some force to make it flex .
Cheers
Kim
As far as ridgidity is concerned , the prepreg cf tubes that i get from my supplier have an 80% unidirectional(longitudinally) fibre content , and a sligthly higher fibre-to-resin ratio than can be achieved by the pulwining/pultrusion process . As for the stiffness of bits from a fishingrod , that would be highly dependent on the diameter and type of rod . That said , a short length as would be necessary for a linear tracking tonearm , 4 to 6 inches for example , would require some force to make it flex .
Cheers
Kim
Niffy,..
You wrote: "place the highest rigidity where the bending moments are greatest and moving the mass closer to center"!
How to determine where are the greatest bending moments without some FEA software? And by "moving the mass closest to center",.. do you think about center of air bearing?
Only few things repels me from making short arm (or no arm at all) is following:
* Having oil damping tank above record.
* Having counterweight above record.
and,... making whole contraption to rotate in order to change record
Now i don't think that 4-5 inch high taper ratio laminated wand would introduce resonances as they are introduced in "normal" 9-12 inch tangential tonearm since this one would be shorter with same mass thus would shift these resonances to a higher frequencies
Am i right?
Niffy, your rolling carriage is clock work I would go nuts with all these small parts and smash everything to oblivion 
You wrote: "place the highest rigidity where the bending moments are greatest and moving the mass closer to center"!
How to determine where are the greatest bending moments without some FEA software? And by "moving the mass closest to center",.. do you think about center of air bearing?
Only few things repels me from making short arm (or no arm at all) is following:
* Having oil damping tank above record.
* Having counterweight above record.
and,... making whole contraption to rotate in order to change record
Now i don't think that 4-5 inch high taper ratio laminated wand would introduce resonances as they are introduced in "normal" 9-12 inch tangential tonearm since this one would be shorter with same mass thus would shift these resonances to a higher frequencies
Am i right?
Niffy, your rolling carriage is clock work
I would go nuts with all these small parts and smash everything to oblivion Hi Zz,
The centre I was referring to is the centre of mass, this is close to (just in front of) the centre of the bearing/vertical pivot. Generally speaking a tapered tube is better. Determining the best amount of taper and the shape of the taper (straight, exponential, elliptic) would require either FEA or a lot of experimentation. I created my own analysis program in excel when designing my carriage. Apart from moving rigidity to where it's needed most and mass away from its needed least tapering has the added benefit that hoop resonance is largely eliminated as the tube diameter varies along its length.
I firmly believe that the sonic benefits of a very short arm more than outweigh the disadvantages of having the pivot and counterweight above the record. If you employ a good clamping system these disadvantages pretty much go away anyway. I admit that I also have reservations about having an open trough of silicone above the record but many many people use this system (Townsend Rock, most commercial air bearing arms, Jim) without issue so I'm probably projecting. Having said that, reducing your arm length to your proposed amount will almost certainly be beneficial.
My carriage actually has a relatively simple shape, developed to minimize resonance. It was however quite complicated to construct and I admit to swearing at it on numerous occasions.
Your diagram looks a lot like a Kuzma airline which is a great arm and a good place to start.
Niffy
The centre I was referring to is the centre of mass, this is close to (just in front of) the centre of the bearing/vertical pivot. Generally speaking a tapered tube is better. Determining the best amount of taper and the shape of the taper (straight, exponential, elliptic) would require either FEA or a lot of experimentation. I created my own analysis program in excel when designing my carriage. Apart from moving rigidity to where it's needed most and mass away from its needed least tapering has the added benefit that hoop resonance is largely eliminated as the tube diameter varies along its length.
I firmly believe that the sonic benefits of a very short arm more than outweigh the disadvantages of having the pivot and counterweight above the record. If you employ a good clamping system these disadvantages pretty much go away anyway. I admit that I also have reservations about having an open trough of silicone above the record but many many people use this system (Townsend Rock, most commercial air bearing arms, Jim) without issue so I'm probably projecting. Having said that, reducing your arm length to your proposed amount will almost certainly be beneficial.
My carriage actually has a relatively simple shape, developed to minimize resonance. It was however quite complicated to construct and I admit to swearing at it on numerous occasions.
Your diagram looks a lot like a Kuzma airline which is a great arm and a good place to start.
Niffy
I thought the same. Before sliding the smaller OD tube into the larger ID tube, I would coat the outside of smaller tube with epoxy resin.
Hello
This is my fast vector sketch of my linear tonearm
usually i do Rhino 3D but for now i dont have to much free time for this.
Anyway all is pretty much in scale. Ah yes platter is 32 CM not mm
Cheers
Zz
[/URL][/IMG]
Looks nice! For aluminum alloy, I would suggest 2024. It sounds better than regular 6061 aluminum. Or you may use magnesium as well.
Epoxy/glue
Consider the viscosity ; the thinnest epoxy-resin i can think of is "Git-rot" (no affiliation). It works by capillary action , which would come in quite handy considering the tight fit of the tubes within each other . It doesn't set quite as hard as some of the boatbuilding epoxies i use now . Unfortunately i can't seem to find it here in Europe , so i heat my epoxy-resin carefully while mixing and get similar results . Another way of bonding the tubes to each other would be by using a polyurethane sealing/bonding compound which retains a certain degree of elasticity after curing . There are countless types on the market ; i haven't tried this myself yet , but i guess that cautiously heating/thinning could be helpfull here too . I think you can achieve a little isolation of the individual tubes , certainly plenty of room for experiments .
By the way , do exercise caution when heating epoxies , as runaway reactions , also known as exothermic reactions are always a possibility . Masks and gloves are mandatory , an allergic reaction to epoxies is not to be taken lightly .
Cheers
Kim
Consider the viscosity ; the thinnest epoxy-resin i can think of is "Git-rot" (no affiliation). It works by capillary action , which would come in quite handy considering the tight fit of the tubes within each other . It doesn't set quite as hard as some of the boatbuilding epoxies i use now . Unfortunately i can't seem to find it here in Europe , so i heat my epoxy-resin carefully while mixing and get similar results . Another way of bonding the tubes to each other would be by using a polyurethane sealing/bonding compound which retains a certain degree of elasticity after curing . There are countless types on the market ; i haven't tried this myself yet , but i guess that cautiously heating/thinning could be helpfull here too . I think you can achieve a little isolation of the individual tubes , certainly plenty of room for experiments .
By the way , do exercise caution when heating epoxies , as runaway reactions , also known as exothermic reactions are always a possibility . Masks and gloves are mandatory , an allergic reaction to epoxies is not to be taken lightly .
Cheers
Kim
Niffy,..
Sure it is similar to Air line but,..
Kuzma Air line is unnecessary high in order to mount wand on/above bearing clamp,. That why it have this strange headshell. I am thinking that it will unnecessary introduce stability issues on full setup. It is higher than mine for full diameter of arm tube, and his arm tube is big on diameter. All other is self reasoning and it cant be simpler than that.
I will admit that i am ready to give away these small nuances in sound difference to have more friendly rig for music listening and will continue to work on 3D CAD-CAM models of these parts, though i have a question for you guys:
What would be measurements for height of highest cartridges so i can later use smaller ones with shims?
Super,...
In order to achieve same bond of two tubes lengthwise you need to coat inner side of larger tube and outer side of smaller tube before pushing/gluing than wipe excess of glue. Otherwise glue will be removed by outer tube edge when you push inner tube inside and
glue will be nonuniform lengthwise.
Zz
Sure it is similar to Air line but,..
Kuzma Air line is unnecessary high in order to mount wand on/above bearing clamp,. That why it have this strange headshell. I am thinking that it will unnecessary introduce stability issues on full setup. It is higher than mine for full diameter of arm tube, and his arm tube is big on diameter. All other is self reasoning and it cant be simpler than that.
I will admit that i am ready to give away these small nuances in sound difference to have more friendly rig for music listening and will continue to work on 3D CAD-CAM models of these parts, though i have a question for you guys:
What would be measurements for height of highest cartridges so i can later use smaller ones with shims?
Super,...
In order to achieve same bond of two tubes lengthwise you need to coat inner side of larger tube and outer side of smaller tube before pushing/gluing than wipe excess of glue. Otherwise glue will be removed by outer tube edge when you push inner tube inside and
glue will be nonuniform lengthwise.
Zz
Thanx Super,..
Magnesium is out of my picture and i will stick with Alu alloys. It is cheaper and easier to get. I never worked with 2000 series alu alloys.Only 6000 and 7000 series. Is 2000 series alu good for inner threads?
Zz
Soendervig,..
I use a lot of epoxy resins in my RC model builds and learn that do not heat while mix or heat already mixed but other solution would be to put packages in hot water bucket for some period of time and than mix and use,.. you will have more pot life.
I find that R+G is very good epoxy resin. I use it a lot
Cheers
Zz
I use a lot of epoxy resins in my RC model builds and learn that do not heat while mix or heat already mixed but other solution would be to put packages in hot water bucket for some period of time and than mix and use,.. you will have more pot life.
I find that R+G is very good epoxy resin. I use it a lot
Cheers
Zz
Heating the epoxy resin is definitively helpful. I made an all carbon fiber head shell and sank it in epoxy resin for about an hour.
This is where I got my epoxy.
Fiberglass , Epoxy , Composites, Carbon Fiber - U.S. Composites, Inc.
Then, I placed it in oven and heated it at temperature 180 F. The head shell was pretty hard. However, I don’t use the carbon fiber head shell now because I found aluminum suits my preference more.
Jim
I did the inner threads manually and didn’t have any problems. I got my magnesium from eBay
Magnesium Metal Ingot 99.95% Pure 20+ Ounces, Free Shipping! | eBay
It was painful for me to process the whole piece of magnesium since I don’t have access to a machine shop. Anyway, I did it. It is not too expensive.
Magnesium Metal Ingot 99.95% Pure 20+ Ounces, Free Shipping! | eBay
It was painful for me to process the whole piece of magnesium since I don’t have access to a machine shop. Anyway, I did it. It is not too expensive.
Super,...
Pure magnesium is very dangerous
Are you sure it is 99.95% purity?
Dangerous in terms of what? I had face mask on when I was cutting the magnesium. I am not sure the purity.
Super,...
Pure magnesium is very dangerous
Are you sure it is 99.95% purity?
I don't know much about machining magnesium , but i've heard that it can be nasty stuff to handle . If you're looking for a magnesium headshell , try to find one of the old Nagaoka headshells , the type that you could adjust azimuth on as well . Rek-O-Kut (no affiliation) is selling a headshell that looks very much like the old Nagaoka , though i'm not sure it's made of magnesium as well.
Cheers
Kim
Super.,,,
High purity magnesium is extremely flammable,,,...
Just excerpt from wiki:
Magnesium metal and its alloys can be explosive hazards; they are highly flammable in their pure form when molten or in powder or ribbon form. Burning or molten magnesium reacts violently with water. When working with powdered magnesium, safety glasses with eye protection and UV filters (such as welders use) are employed because burning magnesium produces ultraviolet light that can permanently damage the retina of a human eye.[37]
Magnesium is capable of reducing water and releasing highly flammable hydrogen gas.
Cheers
Zz
High purity magnesium is extremely flammable,,,...
Just excerpt from wiki:
Magnesium metal and its alloys can be explosive hazards; they are highly flammable in their pure form when molten or in powder or ribbon form. Burning or molten magnesium reacts violently with water. When working with powdered magnesium, safety glasses with eye protection and UV filters (such as welders use) are employed because burning magnesium produces ultraviolet light that can permanently damage the retina of a human eye.[37]
Magnesium is capable of reducing water and releasing highly flammable hydrogen gas.
Cheers
Zz
It is not the head shell. I use magnesium as the head shell attachment on the air bearing.
Jim
Zz,
For your arm, 6061 aluminum may work just fine because you have a carbon fiber arm tube to connect the head shell and the clamp. For my arm, the head shell attaches on the bearing directly. I have tried carbon fiber, 6061 aluminum and magnesium. I found that magnesium is a good balance between aluminum and carbon fiber. 6061 aluminum sounds a bit too “ringing” if you know what I mean. Carbon fiber is very good, too.
Jim
For your arm, 6061 aluminum may work just fine because you have a carbon fiber arm tube to connect the head shell and the clamp. For my arm, the head shell attaches on the bearing directly. I have tried carbon fiber, 6061 aluminum and magnesium. I found that magnesium is a good balance between aluminum and carbon fiber. 6061 aluminum sounds a bit too “ringing” if you know what I mean. Carbon fiber is very good, too.
Jim